Many types of threaded fasteners are known. Commonly, threaded fasteners are provided for specialized applications. In assembly processes, a threaded fastener may be used repeatedly, and small cost increments associated with manufacturing procedures for the fastener, or waste from the manufacturing process, can have significant economic impact.
It is known to provide one piece threaded nut fasteners having an enlarged head and a central shank having a threaded bore for receiving a complementary male fastener component. The shank of the fastener may be received in a tube or pipe end, with the enlarged head of the fastener abutting the end edge of the tube. To securely retain the nut fastener in the end of the tube, to prevent the nut fastener from falling out of the tube, it is known to provide knurling on the outer surface of the shank to engage the inner surface of the tube or pipe.
While being in appearance a relatively simple device, such one-piece threaded nut fasteners have shortcomings. For example, because of common knurling techniques, it is not possible to provide knurling along the complete length of the shank up to the undersurface of the head of the fastener. Knurling tools necessarily leave a small ring that is not knurled at the junction between the shank and the underside of the head. Particularly if the shank portion is short, the unknurled ring at the juncture between the enlarged head and the shank can have a significant impact on the overall retention qualities of the shank in the tube or pipe.
Further, forming a nut fastener of this type as one piece, normally by machining, with an broad head and a much narrower outwardly extending threaded shank, necessarily results in significant material waste during the manufacturing process. If the fastener is to be formed of inexpensive materials, such waste may not be significant. However, if the fastener is to be formed of exotic materials that are expensive, such waste substantially increases the cost of the fastener.
In some applications, it may be acceptable, or, in fact, even desirable to provide the shank and the enlarged head portion from different materials. For example, case hardened knurls and a hardened nut capable of meeting proof load requirements of a hardened bolt may be necessary, with the desirable features of a ductile plate washer associated therewith. To provide such in a one-piece structure is not practical.
As an alternative, a more conventional type washer can be associated with the use of a headed nut and shank. However, a two-piece assembly of this type is inconvenient to use, slowing subsequent assembly processes. The washer can become disassociated from the nut, causing delays in assembly and use.
What is needed in the art is a one-piece nut and plate washer assembly that has improved axial retention in a subsequent assembly, in both compression and tension, and also resistance to rotation. An assembly of this nature having customizable axial retention and resistance to rotation is needed.